It is known that sodium and potassium ions along with water vapor are major contaminants of semiconductor materials and devices, especially integrated circuits. These ions tend to migrate through the device material, especially under an applied bias and in the presence of moisture and a halogen environment. When the ions migrate to a p-n junction, they pick up an elctron and become metallic elements and deposit on the p-n junction. Accumulation of these metals at the junction causes the device to short and fail. It is particularly difficult to control the presence of sodium and potassium ions since they are abundant materials in our general living environment. For example, contamination from fingerprints, residual solder fluxes and other processing salts frequently leave a residue of the ions of these alkali metals, in particular sodium.
Various polymeric silicone resins such as RTV silicone elastomer has been used as an encapsulant or sealant material to protect electronic semiconductor devices from mechanical damage and temperature and humidity effects of the environment. However, in the manufacturing processes employing and preparing the silicone materials used in the preparation of the elastomers, trace amounts of sodium or potassium are almost always present. When the encapsulant is employed on the electronic device these ions tend to migrate as mentioned above, causing device failure. Consequently, a way to eliminate these contaminants or reduce their ability to migrate, especially when used as an integrated circuit encapsulant is needed. Since it is not practical to eliminate these ions from the manufacturing process of the silicones, the technique of ion trapping these contaminants has been employed.
It has been known since 1967 that certain macrocyclicpolyethers known as crown ethers can complex alkali metal cations. This was reported by C. J. Pedersen in J. Amer. Chem. Soc., 89, 7017 (1967) and again by R. N. Green in Tetrahedron Letters, 18, 1793, (1972). These crown ethers were then used by Kaneda et al. as reported in Chemical Abstracts under the title "Semiconductor Sealing Resin Compositions Containing Crown Ethers or Cryptate Ethers as the Alkali Metal Ion Getters," March 1976 at page 39929q. According to Chemical Abstracts, this culminated in Japanese issued Patent No. 76-11377. The particular crown ethers described in that patent, in accordance with Chemical Abstracts, are various 18-crown-6 ethers. While these ethers do somewhat restrict the migration of sodium ions in the silicone resin encapsulant, a significant amount of migration is still present.